1. Field of the Invention
The present invention relates to a data communication system using a network. More specifically, the present invention relates to a method for reducing amount of CPU processing performed in terminals and amount of message data transmitted/received to/from the terminals in signaling processing.
2. Description of the Related Art
As one of major research themes in ubiquitous techniques, there is the so-called sensor network. The sensor network is a technique with which a plurality of terminals (referred to as sensor terminals hereinafter) having sensors (sensors for temperature, humidity, oscillation, acceleration, position, voice, for example) are formed in a radio network, and condition of a specific range is to be judged in a comprehensive manner based on information from each sensor. It is expected apply the sensor networks to various fields.
The sensor terminal is provided with very simple computer resources (referred to as resources hereinafter) such as a processor, a memory, and a radio module along with a sensor so as to be able to participate in a radio network. In order to employ a sensor network, it is necessary to form a network with an enormous number of sensor terminals. Thus, the cost of the sensor terminals occupies a large proportion of the total cost when building a work and life support system. Therefore, it is necessary for the sensor terminals to reduce the resources to be loaded thereon as much as possible in order to cut the cost.
In the meantime, for the sensor terminals to perform data communication, it is necessary to perform signaling between the sensor terminals or between the sensor terminals and a host computer or the like to exchange a communication parameter that is required for a specific communication protocol. However, existing communication protocols such as SIP (Session Initiation Protocol) are developed supposedly for high-spec terminals having abundant resources, such as personal computers and work stations.
Therefore, regarding the conventional sensor terminals, there is a limit in cutting the cost by reducing the resources since it is necessary to secure the resources for enabling communications performed with an existing communication protocol. In order to cut the cost for the sensor terminals, it is necessary to reduce the data amount and the processing amount in signaling so as to be processed by the terminals with the reduced resources.
Meanwhile, a technique for reducing the data amount of messages exchanged between the terminals in signaling is disclosed in following documents. A Document (Non-Patent Document 1: Lars-Erik Jonsson, “RFC 4163: Robust Header Compression (ROHC): Requirements on TCP/IP Header Compression” [online], August 2005, IETF, [Searched on Feb. 14, 2008] <URL: http://www.ietf.org/rfc/rfc4163.txt>) discloses ROHC (Robust Header Compression) algorithm that is a message header compression technique. Another Document (Non-Patent Document 2: M. Garcia-Martin et al., “RFC 3845: The Session Initiation Protocol (SIP) and Session Description Protocol (SDP) Static Dictionary for Signaling Compression (SigComp)”, [online] February 2003, IETF, [Searched on Feb. 14, 2008] <URL: http://www.ietf.org/rfc/rfc3485.txt>) discloses Sig Comp (Signaling Compression) algorithm which compresses the entire message with a text-base signaling protocol such as SIP.
Japanese Unexamined Patent Publication 2002-189707 (Patent Document 1) discloses a technique in which a server judges types of a plurality of data devices and operating conditions, and distributes data according to those. Japanese Unexamined Patent Publication 2004-032176 (Patent Document 2) discloses a technique which reduces data amount by extracting base data from a plurality of numerical value data and calculating a difference value with respect to the base data. Japanese Unexamined Patent Publication 2005-020286 (Patent Document 3) discloses a technique in which a network management device transmits device information through performing signaling between terminals and the network management device in accordance with registration requests from the terminals.
Japanese Unexamined Patent Publication 2005-080249 (Patent Document 4) discloses a technique in which terminals registered to a communication supporting device exchange data with each other safely. Japanese Unexamined Patent Publication 11-122251 (Patent Document 5) discloses a technique in which a message exchange device in an ATM communication system holds call setting control information so as to shorten the time required for communication controls. Japanese Unexamined Patent Publication 11-187068 (Patent Document 6) discloses a technique which reduces the number of giving headers by transmitting data with a common header.
In signaling processing performed between terminals, status of the terminals themselves change every time the terminals exchange a request and a response for the request. Processing related to the changes in the status is a burden particularly for the terminals with reduced resources, which therefore is an obstacle for reducing the resources of the terminals.
However, all the methods disclosed in Non-Patent Documents 1, 2 and Patent Documents 2, 6 are to reduce the data amount of a message exchanged between the terminals in signaling by compressing the data of the message. With theses methods, burden imposed due to changes in the status described above cannot be lightened. In addition, the processing amount is rather increased by the processing performed for compression and decompression. Further, there is no structure mentioned in the Patent Documents 1 and 3-5 for lightening the burden related to the changes in the status.